The motor grader is a very versatile vehicle, which is capable of being adapted with numerous production work implements. Motor graders have steerable front wheels for turning. Because of their length, motor graders have relatively large turning radiuses. An articulated motor grader has a front frame portion that is pivotally connected to a rear frame portion about a vertical axis. The pivotable frame portions are used to provide the articulated motor grader with a tighter turning radius to make it more maneuverable.
Motor graders have long been used for removing snow from roads and other paved surfaces. The center moldboard or snow plow, located behind the front wheels and ahead of the operator's cab on the motor grader is angled in use to cast the snow to one side. Normally, the snow is cast to the right side to place the snow removed from the traffic lane onto the shoulder of the highway being plowed. As a result, high banks of snow can be built up on the shoulder of the road. To alleviate this problem, motor graders can be equipped with an auxiliary snow wing. The snow wing has a second snow plow or snow wing moldboard. The snow wing moldboard typically extends from the right side of the motor grader at an angle to cast snow on the shoulder further to the right to remove it from the edge of the adjacent lane of traffic.
Because the snow wing moldboard extends well beyond the side of the motor grader when in its plowing position, it is necessary to bring the snow wing moldboard in close to the motor grader to permit the motor grader to travel from place to place when not plowing snow. A boom arrangement is typically used to raise and lower the moldboard and to maintain the snow wing moldboard in a fixed roading position close to the side of the motor grader. The forward or leading edge of the snow wing moldboard is located adjacent the trailing right hand end of the center moldboard, which places it along the front frame portion of the articulated motor grader. The rearward trailing end of the snow wing moldboard, on the other hand, is located toward the rear of the motor grader, which places it along the rear frame portion. As a consequence, the leading end of the snow wing is connected to the front frame portion, while the trailing end is connected to the rear frame portion of the motor grader. As those skilled will appreciate, the distance from the connection of snow wing on the front frame portion and the connection on the rear frame portion increases in length when the motor grader articulates to the left.
In prior snow wings, a problem occurs when the motor grader was articulated to the left to make a left-hand turn because of this increase in distance between the front connection and the rear connection. As this distance increases, a downward force is exerted on the boom. As the boom is raised and lowered by a double acting hydraulic cylinder, this force is likewise exerted on the hydraulic cylinder in a direction tending to collapse the cylinder. In order to prevent damage to the snow wing or other components, the operator of the motor grader must be cognizant of this force build-up and continually correct the adjustment of the cylinder as required while the motor grader is being articulated.
The present invention is directed to overcome the problems encountered with the prior snow wing support mechanism by providing a hydraulic system having a pressure relief circuit to prevent the creation of a high force acting to collapse the hydraulic cylinder.